NGC 869 and NGC 884

NGC 869 and NGC 884 comprise the outstanding ‘Perseus Double Cluster’, visible to the naked eye and very nicely seen in binoculars and small telescopes. The mystery remains why Messier did not include these two in his catalogue; the Double Cluster was certainly known by him. Indeed, it was known by both Ptolemy and Hipparchus.

The clusters are one binocular field northwest of eta Persei: binoculars.

Each cluster covers a greater area than the full moon. Of the two, NGC 869 (to the west) is the brighter with more members, perhaps 400 stars compared to about 200 stars for NGC 884.

The two are considered infants, 869 being about 5.6 million years old and 884 only 3.2 million years (although these figures have been the subject of considerable disagreement; the latest studies have concluded that they are both 12.8 million years old).

They have the apparent magnitudes of 5.3 and 6.1 respectively, and the existence of an abundance of interstellar material actually dims the apparent magnitude by at least 1.5m.
     While probably seen with the naked eye, assuming a pristine night sky, the two make a magnificent view in small telescopes: blue-white supergiants predominating with a smattering of orange-red supergiants.

Two fine Struve binaries are in the same field:
      Struve 268: 6.7, 8.5; 131º, 2.7".
      Struve 270; AB (yellow and blue): 7.0, 9.7; 305º, 21.4".

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© 1999-2014 by Richard Dibon-Smith.